Power conversion device including primary inverter, transformer, secondary converter, and controller

A power conversion device comprising:

• first and second terminals connected to a DC power source;
• third and fourth terminals connected to a commercial power system or a load;
• a transformer including a primary winding and a secondary winding that has fifth and sixth terminals;
• an inverter circuit connected between the first and second terminals and the primary winding;
• a converter circuit that includes
• a first switch circuit including a first switch and a first diode connected in parallel with the first switch, the first switch circuit being connected between the third and fifth terminals,
• a second switch circuit including a second switch and a second diode connected in parallel with the second switch, the second switch circuit being connected between the fourth and fifth terminals,
• a third switch circuit including a third switch and a third diode connected in parallel with the third switch, the third switch circuit being connected between the third and sixth terminals,
• a fourth switch circuit including a fourth switch and a fourth diode connected in parallel with the fourth switch, the fourth switch circuit being connected between the fourth and sixth terminals,
• a fifth switch circuit including a fifth switch and a fifth diode connected in parallel with the fifth switch, the fifth switch circuit being connected to the first switch circuit in series between the third and fifth terminals, the fifth diode being reversely connected to the first diode,
• a sixth switch circuit including a sixth switch and a sixth diode connected in parallel with the sixth switch, the sixth switch circuit being connected to the second switch circuit in series between the fourth and fifth terminals, the sixth diode being reversely connected to the second diode,
• a seventh switch circuit including a seventh switch and a seventh diode connected in parallel with the seventh switch, the seventh switch circuit being connected to the third switch circuit in series between the third and sixth terminals, the seventh diode being reversely connected to the third diode, and
• an eighth switch circuit including an eighth switch and an eighth diode connected in parallel with the eighth switch, the eighth switch circuit being connected to the fourth switch circuit in series between the fourth and sixth terminals, the eighth diode being reversely connected to the fourth diode;
• and
• a control circuit that
• when a voltage between the fifth and sixth terminals has a first polarity, controls the first switch to be in ON state during a first ON period and controls the fifth switch to be in ON state during a second ON period longer than the first ON period, the second ON period completely including the first ON period, and
• when the voltage between the fifth and sixth terminals has a second polarity opposite to the first polarity, controls the second switch to be in ON state during a third ON period and controls the sixth switch to be in ON state during a fourth ON period longer than the third ON period, the fourth ON period completely including the third ON period.